1. Field of the Invention
This invention relates generally to production of hydroxyalkyl carbamates from anhydrous ammonia and alkylene carbonates. In particular, this invention relates to the low pressure production of high purity hydroxyalkyl carbamates having alkyl groups with three or more carbon atoms by reacting anhydrous ammonia with alkylene carbonates in an evacuated reaction vessel and in the presence of an initiator. This invention also relates to the production of hydroxybutyl carbamate compositions comprising mixtures of 2-hydroxylbutyl carbamate and 1-hydroxymethyl propyl carbamate.
2. Description of the Related Art
Hydroxyalkyl carbamates, such as hydroxylpropyl carbamate and hydroxybutuyl carbamate, are useful intermediates that find utility as, among other things, components in clear topcoats for automobiles. In the past, hydroxyalkyl carbamates have been produced by the reaction of alkylene carbonates with aqueous ammonia or ammonium hydroxide. Although reaction of alkylene carbonates with aqueous ammonia occurs readily, the purity of resulting hydroxyalkyl carbamate products is typically poor due to hydrolysis reactions that occur in the presence of water. Typical hydrolysis byproducts that reduce the purity of hydroxyalkyl carbamate products include alkylene glycols. Because of these impurities, hydroxyalkyl carbamate products produced using aqueous or aqueous ammonia typically have purity levels that do not exceed about 90%. Such low purity levels render hydroxyalkyl carbamate products produced by this method unsuitable for many end uses. In addition, hydroxyalkyl carbamates typically must be isolated by distillation or the like from aqueous reaction products which result from the reaction of alkylene carbonates and aqueous ammonia.
In an attempt to improve the purity of hydroxyalkyl carbamates, reaction schemes employing alkylene carbonates and anhydrous ammonia have been employed. However, reaction between alkylene carbonates and anhydrous ammonia is typically difficult to to initiate, typically requiring elevated pressures. For example, the reaction of propylene carbonate with anhydrous ammonia typically requires a pressure of about 100-200 psig in order to initiate reaction. This pressure range is unsuitable for commercial production in conventional kettle reactor vessels.